Spectroscopic Gravitational Lens Candidates in the CNOC2 Field Galaxy Redshift Survey

We present five candidate gravitational lenses discovered spectroscopically in the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2), along with one found in follow-up observations. Each has a secure redshift based on several features, plus a discrepant emission line that does not match any known or plausible feature and is visible in multiple direct spectral images. We identify these lines as Lyα λ1216 or [O II] λ3727 emission from galaxies lensed by or projected onto the CNOC2 target galaxies. Einstein radii estimated from the candidate deflector galaxy luminosities indicate that for two candidates the lines are probably [O II] from projected z < 1 galaxies (consistent with the detection of Hβ as well as [O II] in one of them), but that in the remaining four cases the lines could be Lyα from lensed z < 3 galaxies. We estimate that only 1.9 ± 0.7 [O II]–emitting galaxies are expected to project onto target galaxies in the original CNOC2 sample, consistent with three or four of the six candidates being true gravitational lenses.